In recent years, power consumption is increasing in all the electronic devices in association with significant increase in amount of info-communication. In contrast, a switching power source is required to be compact and low in price.
The transformer of this type has a configuration shown in FIGS. 22, 23, 24, 25 and 26.
In other words, as shown in FIG. 22, primary coil 3 and secondary coil 4 are laminated alternately via insulating film 5 on bobbin 2. Then, bobbin 1 is fitted and magnetic core 6 is inserted. FIG. 23 is a cross-sectional view thereof. Lead drawing holes 10 are formed on bobbin 2, and an input and an output to/from primary coil 3 or secondary coil 4 are drawn through lead drawing holes 10 and are connected to pin terminals 9.
FIG. 24 is a perspective view of bobbin 2, and shows positions and shapes of lead drawing holes 10. FIG. 25 shows a state of mounting a coil to a bobbin. As shown in FIG. 25, primary coil 3 assumes a state of a coil, and distal end 13 of drawn lead 12 of primary coil 3 is inserted to a recess of lead drawing hole 10 from above bobbin 2. Then, primary coil 3 is moved downward and inserted into center leg portion 14. Primary coil 3 is inserted to a position shown in FIG. 26.
Such a related art is disclosed, for example, in Japanese Patent Unexamined Publication No. 10-261529. In Japanese Patent Unexamined Publication No. 10-261529, a lead drawing structure in the related art is described.
In the transformer in the related art as described above, when a coil is mounted to a bobbin, a distal end of a drawn lead is entered into a recess of a lead drawing hole of the bobbin and, while maintaining this state, an inner hole of the coil is inserted into a center leg portion of the bobbin. In this state, insertion of the coil is performed while holding the drawn lead so that the drawn lead does not come out from the recess. When the drawn lead is not maintained in a specified recess, there may arise problems such that the bobbin cannot be fitted, it may come into contact with a magnetic core, or it is wired to a wrong pin terminal. When such an event is occurred, a fatal defect is resulted as a transformer. Therefore, the coil inserting operation is performed gradually and deliberately.
Normally, there are a plurality of the coils. Therefore, it is necessary to insert a subsequent coil attentively so as not to apply a stress to cause the drawn lead of the coil which is mounted previously to come out from the recess when inserting the subsequent coil. Therefore, the workability is very low.
When laminating the plurality of the coils, positions of the drawn leads may be displaced according to variation in arrangement of the coils or finished dimension of the coils. Consequently, other lead drawing holes may be occupied by previously inserted coils, whereby there may arise a case in which the drawn lead of the subsequent coil cannot be inserted.
Therefore, the drawn lead must be inserted into the recess while adjusting the position of the drawn lead, and a number of processes of operation are required for correction thereof.